With the recent widespread use of EPS devices, further improvement of product appeal is desired. It is particularly demanded to, in the event of a failure in an EPS device, preserve the steering assist function of the EPS device even for a limited time.
Patent Document 1 discloses a technique to preserve the steering assist function of the EPS device by, upon detection of an abnormality in a torque sensor, generating an alternative signal based on signals from upstream and downstream sides of a torsion bar, switching an output signal of the torque sensor to the alternative signal and continuing steering assist control operation according to the alternative signal.